diff --git a/src/Humanizer.Tests/Humanizer.Tests.csproj b/src/Humanizer.Tests/Humanizer.Tests.csproj
index 5742d610f..8d3ec3eee 100644
--- a/src/Humanizer.Tests/Humanizer.Tests.csproj
+++ b/src/Humanizer.Tests/Humanizer.Tests.csproj
@@ -81,6 +81,7 @@
     <Compile Include="Localisation\bn-BD\TimeSpanHumanizeTests.cs" />
     <Compile Include="Localisation\DefaultFormatterTests.cs" />
     <Compile Include="Localisation\de\CollectionFormatterTests.cs" />
+    <Compile Include="Localisation\es\NumberToWordsFeminineTest.cs" />
     <Compile Include="Localisation\fi-FI\NumberToWordsTests.cs" />
     <Compile Include="Localisation\hr\DateHumanizeTests.cs" />
     <Compile Include="Localisation\nb\DateHumanizeTests.cs" />
diff --git a/src/Humanizer.Tests/Localisation/es/NumberToWordsFeminineTest.cs b/src/Humanizer.Tests/Localisation/es/NumberToWordsFeminineTest.cs
new file mode 100644
index 000000000..6c17f8cca
--- /dev/null
+++ b/src/Humanizer.Tests/Localisation/es/NumberToWordsFeminineTest.cs
@@ -0,0 +1,27 @@
+using Xunit;
+using Xunit.Extensions;
+
+namespace Humanizer.Tests.Localisation.es
+{
+    public class NumberToWordsFeminineTests : AmbientCulture
+    {
+        public NumberToWordsFeminineTests() : base("es-ES") { }
+
+        [Theory]
+        [InlineData(1, "una")]
+        [InlineData(21, "veintiuna")]
+        [InlineData(31, "treinta y una")]
+        [InlineData(81, "ochenta y una")]
+        [InlineData(500, "quinientas")]
+        [InlineData(701, "setecientas una")]
+        [InlineData(3500, "tres mil quinientas")]
+        [InlineData(200121, "doscientas mil ciento veintiuna")]
+        [InlineData(200000121, "doscientos millones ciento veintiuna")]
+        [InlineData(1000001, "un millón una")]
+        public void ToWords(int number, string expected)
+        {
+            Assert.Equal(expected, number.ToWords(GrammaticalGender.Feminine));
+        }
+
+    }
+}
diff --git a/src/Humanizer/Localisation/NumberToWords/SpanishNumberToWordsConverter.cs b/src/Humanizer/Localisation/NumberToWords/SpanishNumberToWordsConverter.cs
index d8ef2d238..97a308a5e 100644
--- a/src/Humanizer/Localisation/NumberToWords/SpanishNumberToWordsConverter.cs
+++ b/src/Humanizer/Localisation/NumberToWords/SpanishNumberToWordsConverter.cs
@@ -8,8 +8,11 @@ internal class SpanishNumberToWordsConverter : GenderedNumberToWordsConverter
         private static readonly string[] UnitsMap = { "cero", "uno", "dos", "tres", "cuatro", "cinco", "seis", "siete", "ocho", "nueve", "diez", "once", "doce", 
                                                         "trece", "catorce", "quince", "dieciséis", "diecisiete", "dieciocho", "diecinueve", "veinte", "veintiuno",
                                                         "veintidós", "veintitrés", "veinticuatro", "veinticinco", "veintiséis", "veintisiete", "veintiocho", "veintinueve"};
+        private const string Feminine1 = "una";
+        private const string Feminine21 = "veintiuna";
         private static readonly string[] TensMap = { "cero", "diez", "veinte", "treinta", "cuarenta", "cincuenta", "sesenta", "setenta", "ochenta", "noventa" };
         private static readonly string[] HundredsMap = { "cero", "ciento", "doscientos", "trescientos", "cuatrocientos", "quinientos", "seiscientos", "setecientos", "ochocientos", "novecientos" };
+        private static readonly string[] FeminineHundredsMap = { "cero", "ciento", "doscientas", "trescientas", "cuatrocientas", "quinientas", "seiscientas", "setecientas", "ochocientas", "novecientas" };
 
         private static readonly Dictionary<int, string> Ordinals = new Dictionary<int, string>
         {
@@ -38,7 +41,7 @@ public override string Convert(int number, GrammaticalGender gender)
             if ((number / 1000000000) > 0)
             {
                 parts.Add(number / 1000000000 == 1
-                    ? string.Format("mil millones")
+                    ? "mil millones"
                     : string.Format("{0} mil millones", Convert(number / 1000000000)));
 
                 number %= 1000000000;
@@ -47,7 +50,7 @@ public override string Convert(int number, GrammaticalGender gender)
             if ((number / 1000000) > 0)
             {
                 parts.Add(number / 1000000 == 1
-                    ? string.Format("un millón")
+                    ? "un millón"
                     : string.Format("{0} millones", Convert(number / 1000000)));
 
                 number %= 1000000;
@@ -56,34 +59,47 @@ public override string Convert(int number, GrammaticalGender gender)
             if ((number / 1000) > 0)
             {
                 parts.Add(number / 1000 == 1
-                    ? string.Format("mil")
-                    : string.Format("{0} mil", Convert(number / 1000)));
+                    ? "mil"
+                    : string.Format("{0} mil", Convert(number / 1000, gender)));
 
                 number %= 1000;
             }
 
             if ((number / 100) > 0)
             {
-                parts.Add(number == 100 ? string.Format("cien") : HundredsMap[(number / 100)]);
+                parts.Add(number == 100 
+                    ? "cien"
+                    : gender == GrammaticalGender.Feminine 
+                        ? FeminineHundredsMap[(number / 100)]
+                        : HundredsMap[(number / 100)]);
                 number %= 100;
             }
 
             if (number > 0)
             {
                 if (number < 30)
-                    parts.Add(UnitsMap[number]);
-                else if (number > 20 && number < 30) {
-                    var lastPart = TensMap[number / 10];
-                    if ((number % 10) > 0)
-                        lastPart += string.Format(" {0}", UnitsMap[number % 10]);
-
-                    parts.Add(lastPart);
+                {
+                    if (gender == GrammaticalGender.Feminine && (number == 1 || number == 21))
+                    {
+                        parts.Add(number == 1 ? Feminine1 : Feminine21);
+                    }
+                    else
+                    {
+                        parts.Add(UnitsMap[number]);
+                    }
                 }
                 else
                 {
-                    var lastPart = TensMap[number / 10];
-                    if ((number % 10) > 0)
+                    var lastPart = TensMap[number/10];
+                    int units = number%10;
+                    if (units == 1 && gender == GrammaticalGender.Feminine)
+                    {
+                        lastPart += " y una";
+                    }
+                    else if (units > 0)
+                    {
                         lastPart += string.Format(" y {0}", UnitsMap[number % 10]);
+                    }
 
                     parts.Add(lastPart);
                 }